Bicycle Detection at Traffic

Actuated Signals

Presented to the AB 1581 Subcommittee of the California Traffic Control Devices Committee

March 4, 2008

Robert M. Shanteau, PhD, PERegistered Traffic Engineer

13 Primrose CirSeaside, CA 93955-4133

Voice: (831) 394-9420FAX: (831) 394-6045

email: RMShant@gmail.com

Photo: Bob Sutterfield

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Robert M Shanteau, PhD, PE

• Registered Traffic Engineer

• B.S. Physics, 1970, San Jose State University

• Ph.D. Transportation Engineering, 1980, UC Berkeley

• Chair, ITE Committee 4A-36, Location of Detector Loopsto Reduce Congestion at Intersections, 1990

• Author, Using Cumulative Curves to Measure Lost Timeand Saturation Flow, ITE Journal, October 1988

• Instructor, Traffic Signal Equipment and Operations, UCBerkeley ITS Extension, 1994

• Instructor, Traffic Congestion Management, UC BerkeleyITS Extension, 1990

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AB 1581, Fuller

• Addresses problem that has existed since inductive loopdetectors were introduced in 1960's

• Signed by Governor Schwarzenegger on October 8, 2007

• Bicyclists and motorcyclists are legitimate users ofroadways in California

• Requires all new and replaced traffic signals to detectbicycle or motorcycle traffic

• Will take effect when Caltrans adopts uniform standards,specifications, and guidelines for the detection of bicycleand motorcycle traffic and related signal timing

• Incremental costs of installing sensor wiring subject toState Mandates provisions

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Caltrans implementation plan

• Caltrans presents its standards for bicycle detection andits approach for developing standards for bicycle timingto CTCDC (today)

• Caltrans amends scope of PATH project on bicycledetection to add testing of bicycle green interval

• PATH project complete June 2008

• Caltrans adds Action item to Aug 2008 CTCDC agenda

• Caltrans presents final standards on bicycle detection foradoption at April 2009 CTCDC meeting

• Caltrans publishes final bicycle detection and signaltiming standards as amendment to next revision ofCalifornia MUTCD, expected in 2010

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But bicyclists have problems being detected NOW

• Caltrans to install Type D loops or video detection forbicycle detection at new & modified actuated signals

• Bicyclists must wait until 2010 for changes to all actuatedsignals in California, state or local

• Knowledge exists of how to detect bicycles with loops• Bicyclists need to know where to stop when they cannot

see the loop• To be detected by a loop a bicycle’s rim must be made of

metal or have a loop of wire around non-metallic rim• The problem of bicycles not being detected at actuated

signals needs to be addressed immediately and not bepostponed for research on extended green intervals

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Caltrans plans no new research into loops

• Strategic direction is to move away from in-pavementdetection

• Future research to focus primarily on video systems andother out-of-pavement detection (PATH project)

• Reasons to stop using loops include safety of work crews,congestion, and cost

• Caltrans believes it is difficult to detect narrow objectssuch as bicycles

• Another reason is that bicycles are increasingly made ofnon-metallic materials

• Caltrans is seeking solution that is 100% effective whenbicyclists are now detected less than 25% of time

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Can bicycles be detected with loops?

• Magnetic field in a wire is in a circlearound the wire

• Left-right horizontal magnetic fieldintersects the rims at a right angle

• If rim is metal, thenbicycle will bedetected

• If rim is not metal,then bicyclist needsto wrap several turnsof copper wirearound rim Best places for bicycle to be

detectedWorst place for bicycleto be detected

Drawing: Dan Gutierrez

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The bicyclist’s nightmare: the invisible loop

• A bicycle that is just a short distance from the sawcut isnot detected

• Standard Specification 86-5.01A(5) states, “If asphaltconcrete surfacing is to be placed, the loop conductors shallbe installed prior to placing the uppermost layer of asphaltconcrete.”

• Bicycle Detector Symbol (2006 California MUTCDSection 9C.05) located over a sawcut shows thebicyclist where to stop

• For practical, financial and institutional reasons,deployment of Bicycle Detector Symbols isrelatively rare

Drawing: Caltran

s Stan

dard Plan A24

C

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Type D loops

• Diagonal quadrupole

• Can detect bicycles across itswidth because it has somehorizontal magnetic fieldeverywhere within the loop

• It does an excellent job ofrejecting vehicles in adjacent lanes

• If a Type D loop is built larger than 6' and located closeto the lane line then bicyclists are more likely to stopover it (but need research to know how large is OK)

• A large Type D loop almost as wide as the lane wouldnot need a Bicycle Detector Symbol

Drawing: Caltrans Standard Plan ES‐5B

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Caltrans has decided to retrofit with Type D loops

• But the standard Type D loop is only 6 feet wide

• 3 feet between loop and lane stripe remains undetected

• Type D loop has four acute angles, which need to berounded off to prevent damage to the conductors

• Acute angles cause premature pavement failure and areto be avoided

• The Type D loop is more complex and thus moreexpensive to install than the Type A, B or E loop

• Division of Research and Innovation (DRI) says, “Currently, wherever applicable, bicycle detection isinstalled using the Type D inductive loop. The Type D loopis very expensive to install and hard to maintain”

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Other diagonal quadrupoles

• Add 1 or 2 diagonal sawcuts to Type A,B or E loops

• Type E with diagonal sawcut(s) is calleda “quadracircle” (or “quadrocircle”)

• Quadracircle being used in Palo Alto,Cupertino and Monterey

• Quadracircle mentioned in“Implementing Bicycle Improvements atthe Local Level,” FHWA-98-105, 1998

• Quadracircle has similar characteristicsto Type D, but is cheaper to install, lesscomplex, and has no sharp acute angles

As specified45 degrees

S

F

Type A diagonal quadrupoleAs specified

45 degrees

S

F

Type B diagonal quadrupole

5/8" width cut

As specified

2" core b it cuts

45 degrees

SF

Type E diagonal quadrupole“quadracircle”

5/8" width cut

As specified

2" core b it cuts

45 degrees

SF

1'0"

Type E diagonal quadrupolewith 2 diagonal sawcuts

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Drawing: Figure 4D‐111(CA), California MUTCD

Locating loops where bicyclists are expected to stop

• At signalized intersections,bicyclists may use left turnlanes to turn left andthrough lanes to continuestraight

• Figure 4D-111(CA) fromthe 2006 CaliforniaMUTCD shows bicycleloops centered in eachtravel lane as well as thebike lane, but bicycle loopsin travel lanes are toonarrow

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Recommendations

1. Immediately require Bicycle Detector Symbols at alltraffic actuated signals

2. Eventually retrofit all traffic actuated signals either withdiagonal quadrupole as the head loop, appropriatelylocated and sized, or out-of-pavement bicycle detection

3. Educate bicyclists and bicycle manufacturers of need touse several turns of wire on non-metal bicycle wheels

4. Include diagonal quadrupole loops in future research

5. Include additional diagonal quadrupole loops (e.g.,quadracircle) on Caltrans standard plans

6. Continue research into inductive loops, out-of-pavementdetection and extended green intervals for bicyclists